Polyurethane or polyurethane (PU)

Polyurethane or polyurethane or polyurethanes refers to a class of chemicals that are made from the reaction of polyols and isocyanates as the main constituents.

History of polyurethane:

These materials with special properties were very advanced in various industries in the world. The first polyurethanes were produced by the reaction of diisocyanate. Alitanes are compounds that have a urethane bond in their structure. Polyurethane (PU) is the general name for polymers that have a urethane bond. The urethane bond is formed by an additive reaction between an isocyanate group and an active hydrogen compound such as a hydroxyl group. Isocyanate groups are highly reactive and therefore do not require temperature increase to develop their reaction. (The reaction takes place at ambient temperature) The most important feature of this group of polymers is that a stable structure is formed after the reaction.
Polyurethane can be produced in various forms such as foam products, films, elastomers, powders, liquids and emulsions.

Application of polyurethanes:

Polyurethanes in various forms including soft foams, shoe and shoe soles, hard foams; Elastomers, thermoplastic elastomers, resins, paints, coatings, adhesives, types of coolants, etc. are used in the world. One of the applications of polyurethanes is to be used as a cover for pipes buried in the soil in order to protect against corrosion. The polyurethane used in this method is 100% solid and with two-component raw materials, but one should not expect much adhesion to the surface of the pipe from this coating. Polyurethanes are used in special applications such as high pipeline temperatures or overhaul repairs and are less commonly used as the main coating of transmission lines. The use of polyurethane coatings for the inner coating of transmission lines has a very limited application and is not recommended for the inner coating due to the release of toxic isocyanate compounds.
Polyurethanes have excellent resistance to impact abrasion and cracking, including fast and complete curing at room temperature. Aliphatic polyurethanes are more expensive than aromatic types. That is why aromatic types and epoxy samples are used in primers, base paints and interface coatings. While aliphatics are specific to the final coating. The use of protective coatings to prevent corrosion in steel structures with primers and base coatings of epoxy systems are examples of important applications of polyurethanes. Another case is floor covering systems in which all kinds of base coatings can be used, sometimes the final urethane coating is sufficient for the final floor layer.

Compounds that have the isocyanate group are:

  • 2, 4 or 2 and 6 toluene di isocyanate
  • 4, 4 or 2 and 4 diphenyl methane di isocyanate
  • 1 and 6 hexamethylene diisocyanate

In addition to the above, there are other isocyanate compounds. Compounds that have two groups of hydroxyl (OH) or more are called polyols, and the following types are commonly used:

  • Polyester Polyol
  • Polyester Polyol
  • Polycarbonate Polyol
  • Polycaprolactone Poly L.

In addition,

instead of hydroxyl groups, compounds such as carboxylic acids and amines, which contain active hydrogen, can also be used in combination with isocyanates. For this reason, when it comes to polyurethanes, we can say that there are countless varieties of them. From what has been said, it can be concluded that polyurethanes are used in various applications such as: soft foams, hard foams, elastomers, adhesives, coatings and colored bases.